preferences: Replace "Disable notifications" with "Desktop notifications"

Because inverse-logic options are evil and this was the only one in the
entire Preferences dialog anyway.

changelog

@@ -277,6 +277,8 @@ Version 1.13.0-dev:
    * Enabled action icons in the hotkey preferences dialog.
    * Fix bug #21717: "F5->reload wml tree" doesn't work in editor.
    * Fix bug #21298: Minimap shows invisible overlays
+   * Replaced "Disable notifications" in Preferences -> Advanced with a new
+     "Desktop notifications" option that defaults to enabled.
 
 Version 1.11.11:
  * Add-ons server:

data/advanced_preferences.cfg

@@ -116,10 +116,10 @@
 [/advanced_preference]
 
 [advanced_preference]
-    field=disable_notifications
-    name= _ "Disable notifications"
+    field=desktop_notifications
+    name= _ "Desktop notifications"
     type=boolean
-    default=no
+    default=yes
 [/advanced_preference]
 
 [advanced_preference]

players_changelog

@@ -75,6 +75,8 @@ Version 1.13.0-dev:
    * Fix bug wherein "lobby sounds" advanced preference didn't do anything for the default lobby.
    * Fix bug wherein dbus notifications did not have a wesnoth icon
    * Fix bug wherein chat history synopses weren't working right in the dbus notifications
+   * Replaced "Disable notifications" in Preferences -> Advanced with a new
+     "Desktop notifications" option that defaults to enabled.
 
 Version 1.11.11:
  * Campaigns:

src/desktop/notifications.cpp

@@ -55,7 +55,7 @@ bool available() { return true; }
 
 void send(const std::string& owner, const std::string& message, type t)
 {
-	if (preferences::get("disable_notifications", false)) { return; }
+	if (!preferences::get("desktop_notifications", true)) { return; }
 
 	Uint8 app_state = SDL_GetAppState();